Variable displacement mechanism for scroll type compressor

ABSTRACT

In a scroll type compressor having a movable scroll member and a fixed scroll member, the movable scroll member and the fixed scroll member defines compression chambers therebetween. The compression chambers reduce in volume in accordance with orbital motion of the movable scroll member relative to the fixed scroll member. Thus gas is compressed. A variable displacement mechanism for the scroll type compressor has a by-pass passage, a pivotal plate and an actuator. The by-pass passage serves to interconnect the compression chamber in a process of volume-reducing and a suction pressure region. The pivotal plate has a communication hole that partially constitutes the by-pass passage and is selectively pivoted between a first pivotal position for opening the by-pass passage by the communication hole and a second pivotal position for closing the by-pass passage. The actuator serves to pivot the pivotal plate.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a scroll type compressor for usein a vehicle air conditioner and more particularly to a variabledisplacement mechanism for varying the displacement of the scroll typecompressor.

[0002] A variable displacement mechanism of such type is, for example,disclosed in Unexamined Japanese Patent Publication No. 2001-32787. Acompression chamber communicates with a suction pressure region througha by-pass passage in the process of volume-reducing. A spool valve opensand closes the by-pass passage to optionally vary the displacement ofthe scroll type compressor.

[0003] In the spool valve, a spool is slidably accommodated in acylinder. The spool has an outer diameter that is substantially equal tothe inner diameter of the cylinder and includes a rod for partiallyconstituting the by-pass passage.

[0004] An unwanted feature is that the spool valve of the variabledisplacement mechanism is configured to open and close a port that opensat the inner circumferential surface of the cylinder (the inner surfaceof the cylinder) by a valve portion (a column) of the spool so that itis difficult to arrange a seal member at the valve portion. Therefore,the valve portion of the spool contacts the inner circumferentialsurface of the cylinder so as to prevent refrigerant gas from leakingfrom the spool valve.

[0005] A small clearance between the valve portion of the spool and theinner circumferential surface of the cylinder effectively suppresses theleakage of the refrigerant gas from the by-pass passage. However, as theclearance between the valve portion of the spool and the innercircumferential surface of the cylinder is small, sliding resistanceincreases between the spool and the cylinder. Consequently, problemssuch as deterioration in response to displacement variation andenlargement of an actuator for actuating the spool are arisen.

[0006] Accordingly, in a prior art, in view of suppressing the rise ofcost for manufacturing the highly accurate clearance, the clearancebetween the valve portion of the spool and the inner circumferentialsurface of the cylinder is relatively large. Then, for example, even ifthe scroll type compressor is tried to operate at the maximumdisplacement by closing the by-pass passage, the leakage from the spoolvalve (the by-pass passage) becomes an obstacle to achieving a desiredmaximum displacement. Namely, deterioration in performance of the scrolltype compressor has arisen. Therefore, there is a need for a variabledisplacement mechanism that reliably seals a by-pass passage for ascroll type compressor.

SUMMARY OF THE INVENTION

[0007] In accordance with the present invention, in a scroll typecompressor having a movable scroll member and a fixed scroll member, themovable scroll member and the fixed scroll member defines compressionchambers therebetween. The compression chambers reduce in volume as theymove in accordance with orbital motion of the movable scroll memberrelative to the fixed scroll member. Thus gas is compressed. A variabledisplacement mechanism for the scroll type compressor has a by-passpassage, a pivotal plate and an actuator. The by-pass passage serves tointerconnect the compression chamber in a process of volume-reducing anda suction pressure region. The pivotal plate has a communication holethat partially constitutes the by-pass passage and is selectivelypivoted between a first pivotal position for opening the by-pass passageby the communication hole and a second pivotal position for closing theby-pass passage. The actuator serves to pivot the pivotal plate.

[0008] Other aspects and advantages of the invention will becomeapparent from the following description, taken in conjunction with theaccompanying drawings, illustrating by way of example the principles ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The features of the present invention that are believed to benovel are set forth with particularity in the appended claims. Theinvention together with objects and advantages thereof, may best beunderstood by reference to the following description of the presentlypreferred embodiments together with the accompanying drawings in which:

[0010]FIG. 1 is a longitudinal cross-sectional view of a hybridcompressor according to a preferred embodiment of the present invention;

[0011]FIG. 2 is a cross-sectional view that is taken along the line I-Iin FIG. 1;

[0012]FIG. 3 is a cross-sectional view that is taken along the lineII-II in FIG. 1;

[0013]FIG. 4 is a cross-sectional view that corresponds to FIG. 3 in astate where a pivotal plate is switched to a second pivotal position;and

[0014]FIG. 5 is a cross-sectional view that is taken along the line I-Iin FIG. 1 according to an alternative embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] A preferred embodiment of the present invention will now bedescribed with reference to FIGS. 1 through 4. The preferred embodimentapplies the present invention to a hybrid compressor C that is a scrolltype. The left side and the right side of FIG. 1 respectively correspondto the front side and the rear side of the compressor C.

[0016] The hybrid compressor C will schematically be described at thebeginning.

[0017]FIG. 1 illustrates a longitudinal cross-sectional view of thecompressor C according to the preferred embodiment of the presentinvention. The compressor C partially constitutes a refrigeration cycleof a vehicle air conditioner. The compressor C accommodates acompression mechanism 12 and an electric motor 21 in a housing 11. Apower transmission mechanism 22 is arranged on an outer wall of thehousing 11. The compression mechanism 12 is a scroll type and isconfigured to optionally vary displacement of the compressor C. Thepower transmission mechanism 22 receives power from an (internalcombustion) engine E for traveling a vehicle.

[0018] The compressor C is selectively driven by one of power from theengine E through the power transmission mechanism 22 and power from theelectric motor 21. Thus, with the electric motor 21, air-conditioning(cooling) is optionally enabled during stop of the engine E.Accordingly, the vehicle air conditioner of the preferred embodiment isparticularly appropriate for an idle-stop vehicle or a hybrid vehicle.

[0019] The compressor C will now be described in detail.

[0020] Still referring to FIG. 1, the housing 11 includes a casing 11 aand a cover 11 b. The casing 11 a is cylindrical in shape and has abottom at one end. The cover 11 b is fixedly connected to the rear endof the casing 11 a. The casing 11 a of the housing 11 has a through hole34 at the center of the bottom of the housing 11, and the through hole34 extends through the bottom of the housing 11. A pulley shaft 13 isinserted through the through hole 34 and is rotatably supported by theis housing 11 through a bearing 35 in the through hole 34.

[0021] A shaft support member 31 is fixed near the opening end of thecasing 11 a in the housing 11. A through hole 31 a extends through thecenter of the shaft support member 31. A compressor shaft 19 iscoaxially arranged with the pulley shaft 13 in the housing 11. The rearend of the compressor shaft 19 is inserted into the through hole 31 a ofthe shaft support member 31 and is rotatably supported by the shaftsupport member 31 through a bearing 32 in the through hole 31 a. Thefront end of the compressor shaft 19 is fitted to the rear end of thepulley shaft 13 through a bearing 33 so as to rotate relative to thepulley shaft 13.

[0022] The power transmission mechanism 22 includes a pulley 17 and anelectromagnetic clutch 18. The pulley 17 is rotatably supported by thehousing 11 and transmits power from the engine E to the pulley shaft 13.The electromagnetic clutch 18, when in an ON-state (energized), permitspower transmission between the pulley 17 and the pulley shaft 13 and,when in an OFF-state (de-energized), disrupts the power transmissiontherebetween.

[0023] A speed increasing mechanism 23 including a planetary gearmechanism is provided between the pulley shaft 13 and the compressorshaft. 19 in the housing 11 for increasing the rotational speed of thepulley shaft 13 and for transmitting the rotation of the pulley shaft 13to the compressor shaft 19. This speed increasing mechanism 23 has aknown structure including a sun gear 45, an internal gear 46, a holder47 and a plurality of planetary gears 48. With the speed increasingmechanism 23, for example, even if the rotational speed of the pulleyshaft13 is relatively low due to an idling state of the engine, thecompressor shaft 19 is rotated at a relatively high speed so as toensure a large amount of refrigerant gas discharged from the compressionmechanism 12 per unit time, that is, to exert a relatively high coolingperformance.

[0024] A stator 15 is provided on the inner circumferential-surface ofthe casing 11 a of the housing 11 and is located on the front side ofhousing 11. A rotor 14 is fixedly connected to the compressor shaft 19in the housing 11 so as to be arranged inside the stator 15. Theelectric motor 21 includes the stator 15 and the rotor 14. The electricmotor 21 integrally rotates the rotor 14 and the compressor shaft 19 bysupplying electric current to the stator 15.

[0025] A fixed scroll member 41 is fixedly accommodated at the openingend of the casing 11 a in the housing 11. The fixed scroll member 41includes a base plate 61 which has a disc-shape, an outer wall 62 whichhas a cylindrical shape and a spiral wall 63. The outer wall 62 extendsfrom the outer periphery of the base plate 61. The spiral wall 63extends from the base plate 61 inside the outer wall 62. The fixedscroll member 41 is fixedly connected to the rear surface of the shaftsupport member 31 at the distal end surface of the outer wall 62.

[0026] A crankshaft 43 is provided at the rear end of the compressorshaft 19 and is located at a position that is offset from an axis L ofthe compressor shaft 19. A bushing 51 is fixedly fitted around thecrankshaft 43. A movable scroll member 42 is supported by the bushing 51through a bearing 52 for rotation relative to the fixed scroll member 41so as to face the fixed scroll member 41. The movable scroll member 42includes a base plate 65 which has a disc-shape and a spiral wall 66that extends from the base plate 65 toward the fixed scroll member 41.

[0027] The fixed scroll member 41 and the movable scroll member 42engage each other by the spiral walls 63, 66 of the fixed and movablescroll members 41, 42, while the distal ends of the spiral walls 63, 66respectively contact the base plates 65, 61 of the movable and fixedscroll members 42, 41. Accordingly, the base plate 61 of the fixedscroll member 41, the spiral wall 63 of the fixed scroll member 41, thebase plate 65 of the movable scroll member 42 and the spiral wall 66 ofthe movable scroll member 42 define compression chambers 67.

[0028] A self-rotation blocking mechanism 68 is interposed between thebase plate 65 of the movable scroll member 42 and the shaft supportmember 31 facing the base plate 65. The self-rotation blocking mechanism68 includes a plurality of cylindrical recesses 68 a and a plurality ofpins 68 b. The cylindrical recesses 68 a are provided at the backsurface (the front surface) of the base plate 65 of the movable scrollmember 42. The pins 68 b are arranged at radially outer portions 64 ofthe shaft support member 31 and are loosely fitted in the respectivecylindrical recesses 68 a.

[0029] A suction chamber 69 is defined between the outer wall 62 of thefixed scroll member 41 and the outermost portion of the spiral wall 66.An accommodating recess 61 b is partially formed at a back surface 61 aof the base plate 61 of the fixed scroll member 41 in the range from theadjacent center portion to the adjacent outer periphery. A dischargehole 61 c is formed through the center of the base plate 61 of the fixedscroll member 41, and the compression chamber 67 near the center of thebase plate 61 communicates with the inner space of the accommodatingrecess 61 b through the discharge hole 61 c. A discharge valve 55constituted of a reed valve is arranged in the accommodating recess 61 bof the fixed scroll member 41 for opening and closing the discharge hole61 c. The opening degree of the discharge valve 55 is regulated by aretainer 56, which is fixedly arranged in the accommodating recess 61 bof the fixed scroll member 41.

[0030] As the compressor shaft 19 is rotated by the engine E or by theelectric motor 21, the movable scroll member 42 orbits around the axis Lof the fixed scroll member 41 through the crankshaft 43 in thecompression mechanism 12. Then, the self-rotation blocking mechanism 68blocks the self-rotation of the movable scroll member 42 and onlypermits the orbital motion of the movable scroll member 42. As themovable scroll member 42 orbits relative to the fixed scroll member 41,the compression chambers 67 are gradually reduced in volume and aremoved from the outer side of the spiral walls 63, 66 of the scrollmembers 41, 42 toward the center side of the spiral walls 63, 66 of thescroll members 41, 42. Thereby, relatively low pressure refrigerant gasintroduced from the suction chamber 69 to the compression chambers 67 iscompressed. The compressed refrigerant gas is discharged from thecompression chamber 67 near the center of the spiral walls 63, 66 to theinner space of the accommodating recess 61 b through the discharge hole61 c by pushing away the discharge valve 55.

[0031] An accommodating chamber 36 is defined in the housing 11 betweenthe base plate 61 of the fixed scroll member 41 and the cover 11 b. Apivotal plate 37 which has a donut-shape is accommodated in theaccommodating chamber 36. The pivotal plate 37 is laid on the backsurface 61 a of the base plate 61 of the fixed scroll member 41. Theopening of the accommodating recess 61 b of the fixed scroll member 41is shut by laying the pivotal plate 37 on the back surface ]o 61 a ofthe base plate 61. Accordingly, the accommodating chamber 36 ispartitioned by the pivotal plate 37 into a discharge chamber 70 and anintroducing chamber 38. The inner space of the accommodating recess 61 bprovides the discharge chamber 70. The space between the pivotal plate37 and the cover 11 b provides the introducing chamber 38 is. Namely,the pivotal plate 37 also serves as a partition wall for partitioningthe accommodating chamber 36 into the introducing chamber 38 and thedischarge chamber 70.

[0032] A support portion 54 which has a cylindrical shape extends fromthe middle portion of the cover 11 b in the accommodating chamber 36. Adistal end surface of the support portion 54 is elongated to contact theback surface 61 a of the base plate 61 of the fixed scroll member 41. Aboss 37 a is provided at the rear surface and the middle portion of thepivotal plate 37. The pivotal plate 37 is rotatably supported by thesupport portion 54 through the boss 37 a.

[0033] As shown in FIGS. 1, 3 and 4, an electromagnetic actuator 60 isarranged in the cover 11 b of the housing 11. The actuator 60 isconfigured to reciprocate a rod 60 b by energizing and de-energizing asolenoid 60 a based upon an external command. A pin 37 d is connected tothe pivotal plate 37, and the rod 60 d of the actuator 60 is operativelyconnected to the pin 37 d. Accordingly, the pivotal plate 37 ispivotally switched between a first pivotal position (a state shown inFIG. 3) and a second pivotal position (a state shown in FIG. 4) byactuating the actuator 60. The first pivotal position is performed by anON-state of the actuator 60 (energizing the solenoid 60 a). The secondpivotal position is performed by an OFF-state of the actuator 60(de-energizing the solenoid 60 a).

[0034] As shown in FIG. 1, a seal member 57 is arranged on the outercircumferential surface of the proximal portion of the support portion54. This seal member 57 serves to seal a contact portion between thesupport portion 54 and the pivotal plate 37 (the boss 37 a) withcylindrical contact region. A seal member 59 is arranged on the backsurface 61 a of the base plate 61 in the fixed scroll member 41 so as tosurround the accommodating recess 61 b. This seal member 59 serves toseal a contact portion between the back surface 61 a of the base plate61 and the pivotal plate 37 with annular contact region. Namely, theseseal members 57, 59 and lubricating oil contained in the refrigerant gasintervene in layer between the support portion 54 and the pivotal plate37 (the boss 37 a) and between the back surface 61 a of the base plate61 and the pivotal plate 37. As a result, the introducing chamber 38 isseparated from the discharge chamber 70.

[0035] An inlet 50 is formed in the outer circumferential wall of thecasing 11 a of the housing 11 so as to correspond with the accommodatingspace for the electric motor 21. An external conduit for connecting withan evaporator of an external refrigerant circuit (not shown) isconnected to the inlet 50. A suction passage 39 is formed at the outercircumferential portion of the shaft support member 31 and the fixedscroll member 41 in the housing 11 for interconnecting the accommodatingregion of the electric motor 21 and the introducing chamber 38.

[0036] A suction hole 61 d is formed at the radially outer portion ofthe base plate 61 of the fixed scroll member 41. The suction hole 61 dopens to the suction chamber 69 at the front end and opens at the backsurface 61 a at the rear end. A suction port 37 b is formed at theradially outer portion of the pivotal plate 37 for interconnecting theintroducing chamber 38 and the suction hole 61 d at any pivotalpositions of the pivotal plate 37. Accordingly, the relatively lowpressure refrigerant gas from the external refrigerant circuit isintroduced into the suction chamber 69 through the inlet 50, the suctionpassage 39, the introducing chamber 38, the suction port 37 b and thesuction hole 61 d.

[0037] The middle portion of the cover 11 b of the housing 11 b forms adischarge passage 58. The front end of the discharge passage 58 extendsthrough the center of the support portion 54 and the center of thepivotal plate 37 (the boss 37 a) and then communicates with thedischarge chamber 70, while an external conduit, which connects acondenser of the external refrigerant circuit (not shown), is connectedto the rear end of the discharge passage 58. Accordingly, the relativelyhigh pressure refrigerant gas in the discharge chamber 70 is dischargedto the external refrigerant circuit through the discharge passage 58.

[0038] As shown in FIGS. 1 through 4, the base plate 61 of the fixedscroll member 41 includes a plurality of by-pass holes 61 e. One end ofeach by-pass hole 61 e opens to the compression chamber 67 that isvolume-reducing, while the other end opens at the back surface 61 a. Aplurality of the by-pass holes 61e is arranged in such a manner thateach of the by-pass holes 61 e alternatively communicates with thecompression chamber 67 that is volume-reducing during times when thecompression chamber 67 at an initial position that is the maximum volumereduces in volume to a predetermined value (for example, 20% of themaximum volume). A plurality of communication holes 37 c extends throughthe pivotal plate 37 in the direction of the axis L so as to correspondwith the by-pass holes 61 e of the base plate 61.

[0039] In the preferred embodiment, the by-pass holes 61 e of the baseplate 61 and the communication holes 37 c of the pivotal plate 37 formby-pass passages (hereinafter the by-pass passages 37 c, 61 e) forinterconnecting the compression chamber 67 that is volume-reducing andthe introducing chamber or a suction pressure region 38. The pivotalplate 37 is pivotally switched between an open position for opening theby-pass passages 37 c, 61 e by the communication holes 37 c and a closeposition for closing the by-pass passages 37 c, 61 e by means of ON/OFFcontrol of the actuator 60.

[0040] Namely, as shown in FIG. 4, each communication hole 37 c of thepivotal plate 37 is offset from the corresponding by-pass hole 61 e ofthe base plate 61 when the pivotal plate 37 is located at the secondpivotal position (the closing position) by turning off the actuator 60.As a result, the by-pass holes 61 e are closed by the plate surface ofthe pivotal plate 37. Accordingly, the compression chamber 67 that isvolume-reducing does not communicate with the introducing chamber 38 andcompletely compresses the refrigerant gas so that the amount ofrefrigerant gas discharged from the compression mechanism 12 per unitrotation, that is, the displacement of the compression mechanism 12,becomes maximum.

[0041] The compression mechanism 12 performs the maximum displacement,for example, when the engine E is selected to drive the compressionmechanism 12. Accordingly, even if the rotational speed of the pulleyshaft 13 is slow due to an idling state of the engine E, the compressionmechanism 12 ensures a large amount of discharged refrigerant gas perunit time, that is, the compression mechanism 12 exercises relativelyhigh cooling performance.

[0042] As shown in FIG. 3, when the pivotal plate 37 is located at thefirst pivotal position (the opening position) by turning on the actuator60, each communication hole 37 c communicates with the correspondingby-pass hole 61 e. Accordingly, the compression chamber 67 that isvolume-reducing constantly communicates with the introducing chamber 38through one of the by-pass holes 61 e and one of the communication holes37 c during times when the volume of the compression chamber 67 that isvolume-reducing is reduced to a predetermined value. As a result, thecompression chamber 67 does not completely compress the refrigerant gasso that the displacement of the compression mechanism 12 reduces incomparison to the maximum displacement.

[0043] The compression mechanism 12 reduces in displacement, forexample, when the electric motor 21 is selected to drive the compressionmechanism 12. As the displacement of the compression mechanism 12reduces, torque required for driving the compression mechanism 12 alsoreduces. Accordingly, the compressor C becomes compact by reducing thesize of the electric motor 21.

[0044] According to the preferred embodiment, the following advantageouseffects are obtained.

[0045] (1) The opening and closing of the by-pass passages 37 c, 61 e,that is, the variation of the displacement of the compressor C, isperformed by pivotally switching the pivotal plate 37. Accordingly,adherence between the pivotal plate 37 and the fixed scroll member 41,on which the pivotal plate 37 slides, seals the by-pass passages 37 c,61 e around the pivotal plate 37. The plate-like member such as thepivotal plate 37 easily enhances adherence with relatively large areaagainst a facing member on which the plate-like member slides incomparison to, for example, the cylindrical member (the valve portion ofthe spool) disclosed in the Unexamined Japanese Patent Publication No.2001-32787. Additionally, a layer of lubricating oil is interposedbetween the pivotal plate 37 and the base plate 61 of the fixed scrollmember 41. Accordingly, the by-pass passages 37 c, 61 e around thepivotal plate 37 are reliably sealed. As a result, the deterioration ofthe performance of the compressor C due to the leakage of therefrigerant gas from the by-pass passages 37 c, 61 e is suppressed.

[0046] (2) The by-pass passage 37 c, 61 e is configured to constantlyinterconnect the compression chamber 67 that is volume-reducing and theintroducing chamber 38 until the volume of the compression chamber 67that is volume-reducing is reduced to a predetermined value when thepivotal plate 37 is switched to the opening position. Namely, thecompression chamber 67 does not completely compress until the volume ofthe compression chamber 67 is reduced to a predetermined value after thecommencement of reducing volume. Accordingly, for example, in comparisonto a variable displacement mechanism that interconnects a compressionchamber that is volume-reducing and a suction pressure region after thecompression chamber compresses until the volume of the compressionchamber is reduced to a predetermined value, power loss of thecompressor C due to re-compression of the refrigerant gas, that is,useless compression work, is suppressed.

[0047] Particularly, in the preferred embodiment, a plurality of theby-pass passages 37 c, 61 e is provided to achieve the above describedconstant communication. Namely, the fixed scroll member 41 provides aplurality of the by-pass holes 61 e. A plurality of the by-pass holes 61e is distributed around the axis L and along the orthogonal directionrelative to the axis L. For example, when a plurality of the by-passholes 61 e is opened or closed by the spool valve as disclosed in theUnexamined Japanese Patent Publication No. 2001-32787, a plurality ofthe spool valves needs to be provided due to the distribution of theby-pass holes 61 e. However, the plate-like pivotal plate 37 of thepreferred embodiment easily forms a plurality of the communication holes37 c distributed around the axis L and along the orthogonal directionrelative to the axis L so as to correspond with the distributed by-passholes 61 e. As a result, the above described constant communication mayeasily be achieved without any complicated structure.

[0048] (3) The pivotal plate 37 is slidably laid on the back surface 61a of the base plate 61 of the fixed scroll member 41. The abovearrangement of the pivotal plate 37 prevents the enlarged compressor Cin the direction of the axis L due to the provision of the variabledisplacement mechanism. In other words, the employment of the plate-likemember such as the pivotal plate 37 for opening and closing the by-passpassages 37 c, 61 e enables universally compact design for laying theplate-like member on the back surface 61 a of the base plate 61 of thefixed scroll member 41.

[0049] Particularly, the compressor C is a hybrid type that isalternatively driven by the power from the engine E through the powertransmission mechanism 22 arranged in the housing 11 or by the powerfrom the electric motor 21 accommodated in the housing 11. Accordingly,the compressor C tends to become large due to the power transmissionmechanism 22 and the electric motor 21. When a compact variabledisplacement mechanism is utilized for the compressor C, increasing sizeof the compressor C is efficiently suppressed.

[0050] (4) The pivotal plate 37 also serves as a partition wall forpartitioning the discharge chamber 70. Accordingly, an exclusivepartition wall is not required for partitioning the discharge chamber 70so that the compressor C is simplified and becomes compact.

[0051] (5) The pivotal plate 37 also serves as a partition wall forpartitioning the introducing chamber 38 and the discharge chamber 70.Accordingly, an exclusive partition wall is not required forpartitioning the introducing chamber 38 and the discharge chamber 70 butthe compressor C is simplified and becomes compact. Furthermore, aportion of the pivotal plate 37 (the side of the back surface) isexposed to the atmosphere in the introducing chamber 38 so that thepivotal plate 37 is easily handled by forming the by-pass passages 37 c,61 e in relatively short.

[0052] (6) The pivotal plate 37 has a donut-shape, and the dischargepassage 58 passes through the center through hole of the pivotal plate37. As a through hole is formed at the center of the pivotal plate 37that is not utilized for opening and closing the by-pass passages 37 c,61 e, the discharge passage 58 is defined to include the through hole.Thus, the radially inner compression chamber 67 and the dischargepassage 58 are interconnected at a minimum distance. Accordingly, gassmoothly flows from the radially inner compression chamber 67 to thedischarge passage 58 so that the compressor C is prevented fromdeteriorating efficiency of the compressor C due to pressure loss basedupon conduit resistance between the compression chamber 67 and thedischarge passage 58.

[0053] The present invention is not limited to the embodiments describedabove but may be modified into the following alternative embodiments.

[0054] The pivotal plate 37 is configured to be pivotally switchedbetween two positions (the first pivotal position and the second pivotalposition) in the preferred embodiment. In other words, the displacementof the compressor C is configured to vary between the maximum and theminimum. In alternative embodiments to those of the above preferredembodiment, the number of pivotal positions is not limited. The pivotalplate 37 is configured to be pivotally switched among three or morepivotal positions and is configured to selectively vary the displacementof the compressor C at an intermediate displacement between the maximumand the minimum.

[0055] The by-pass passages 37 c, 61 e are configured to constantlyinterconnect the compression chamber 67 that is volume-reducing and theintroducing chamber 38 until the volume of the compression chamber 67that is volume-reducing is reduced to a predetermined value when thepivotal plate 37 is switched to the opening position. In alternativeembodiments to those of the above preferred embodiment, the by-passpassages 37 c, 61 e are not limited to the above structure. Referring toFIGS. 1 and 5, the by-pass passages 37 c and 61 e are not formed at theradially outer side of the base plate 61 of the fixed scroll member 41and the pivotal plate 37, respectively but are only formed at theradially inner side of the base plate 61 of the fixed scroll member 41and the pivotal plate 37, respectively, in comparison to the abovedescribed preferred embodiment. In this state, the by-pass passages 37c, 61 e are configured to interconnect the compression chamber 67 thatis volume-reducing and the suction pressure region after the compressionchamber 67 has compressed to reduce in volume to a predetermined value,that is, after the volume of the compression chamber 67 that isvolume-reducing has reduced to a predetermined value. This simplifiesthe structure of the by-pass passage.

[0056] Therefore, the present examples and embodiments are to beconsidered as illustrative and not restrictive, and the invention is notto be limited to the details given herein but may be modified within thescope of the appended claims.

What is claimed is:
 1. A variable displacement mechanism in a scrolltype compressor having a movable scroll member and a fixed scrollmember, the movable scroll member and the fixed scroll member definingcompression chambers therebetween, the compression chambers reducing involume in accordance with orbital motion of the movable scroll memberrelative to the fixed scroll member, whereby gas is compressed, asuction pressure region being defined in the scroll type compressor, thevariable displacement mechanism comprising: a by-pass passage providedfor interconnecting the compression chamber in a process ofvolume-reducing and the suction pressure region; a pivotal plate havinga communication hole that partially constitutes the by-pass passage, thepivotal plate being pivotally switched between a first pivotal positionfor opening the by-pass passage by the communication hole and a secondpivotal position for closing the by-pass passage; and an actuator forpivoting the pivotal plate.
 2. The variable displacement mechanismaccording to claim 1, wherein the by-pass passage is configured toregularly interconnect the compression chamber in the process ofvolume-reducing and the suction pressure region until volume of thecompression chamber in the process of volume-reducing is reduced to apredetermined value in a state where the pivotal plate is switched tothe first pivotal position.
 3. The variable displacement mechanismaccording to claim 1, wherein the by-pass passage is plurally formed. 4.The variable displacement mechanism according to claim 3, wherein thescroll type compressor includes a rotary shaft that has a central axis,the by-pass passages being distributed around the central axis and alongan orthogonal direction relative to the central axis.
 5. The variabledisplacement mechanism according to claim 1, wherein the by-pass passageis configured to interconnect the compression chamber in the process ofvolume-reducing and the suction pressure region after the volume of thecompression chamber in the process of volume-reducing has been reducedto a predetermined value in a state where the pivotal plate is switchedto the first pivotal position.
 6. The variable displacement mechanismaccording to claim 1, wherein the fixed scroll member includes a baseplate and a spiral wall that extends from the base plate, the pivotalplate being slidably laid on a back surface of the base plate.
 7. Thevariable displacement mechanism according to claim 6, wherein the backsurface of the base plate of the fixed scroll member includes anaccommodating recess, a discharge hole opening to the accommodatingrecess for communicating with the compression chamber near a center ofthe spiral wall, a discharge chamber being defined in such a manner thatthe accommodating recess is closed by laying the pivotal plate on theback surface of the base plate.
 8. The variable displacement mechanismaccording to claim 7, wherein the suction pressure region is defined ona side that is opposite to a side of the base plate relative to thepivotal plate, the pivotal plate serving as a partition wall forpartitioning the suction pressure region and the discharge chamber. 9.The variable displacement mechanism according to claim 7, wherein thepivotal plate has a donut-shape, a through hole being formed at thecenter of the pivotal plate, a discharge passage extending through thethrough hole for discharging the gas in the discharge chamber.
 10. Thevariable displacement mechanism according to claim 9, wherein adherencebetween the pivotal plate and the fixed scroll member seals the by-passpassage.
 11. The variable displacement mechanism according to claim 10,wherein a layer of lubricating oil is interposed between the pivotalplate and the base plate of the fixed scroll member.
 12. The variabledisplacement compressor according to claim 1, wherein the scroll typecompressor is used for a vehicle air conditioner, the scroll typecompressor being a hybrid type that is selectively driven by power froman engine for traveling a vehicle and by power from an internal electricmotor.